Year	Percent
1990	27.78
1991	27.76
1992	27.76
1993	27.76
1994	27.75
1995	27.75
1996	27.74
1997	27.74
1998	27.73
1999	27.73
2000	27.71
2001	27.73
2002	27.74
2003	27.75
2004	27.77
2005	27.79
2006	27.9
2007	28.02
2008	28.12
2009	28.21
2010	28.32
2011	28.61
2012	28.93
2013	29.22
2014	29.52
2015	29.82